1. Field of the Invention
The present invention relates to an image forming apparatus using a toner for use in developing an image formed by electrophotography, electrostatic recording, etc., as a developing agent.
2. Discussion of the Background
An image forming apparatus typically includes processes of, for example, uniformly charging the image formation area on the surface of an image bearing member, irradiating the surface of the image bearing member for writing, developing an image on the image bearing member with a frictionally charged toner (developing agent), transferring the image on the image bearing member to a recording medium directly or indirectly via an intermediate transfer body, and fixing the image on the recording medium. Residual toner remaining on the image bearing member which has not been transferred is scraped from the image bearing member in a cleaning process and used in the next image formation process.
As the developing agent, there are a two-component developing agent containing toner and carrier and a single-component developing agent containing magnetic or non-magnetic toner. These toners are typically manufactured by melting, mixing and kneading a resin, a coloring agent, a charge control agent, and a releasing agent, cooling down the mixture and pulverizing and classifying the resultant. However, it is difficult to control the particle size and the form of the toner obtained by this method.
In this situation, studies and development have been made to solve this problem by intentionally controlling the particle size of toner in recent years and methods of toner polymerization, for example, an emulsification polymerization method and a dissolution suspension method, in which granulation is made in an aqueous phase, have become popular.
In addition, the demand for quality images has been increasing in recent years. Reducing and uniforming the particle size of toner are also demanded especially to obtain high definition images in the color image formation. When images are formed with toner having a wide particle size distribution, fine powder toner may scatter and contaminate a development roller, a charging roller, a charging blade, an image bearing member, carrier, etc. Therefore, it is difficult to produce quality images with high reliability by such toner. To the contrary, small toner particles that have a sharp particle size distribution have good development behavior, which leads to great improvement on minute dot reproducibility.
However, toner having a small particles diameter and a sharp particle size distribution has a problem with regard to the cleaning property. Especially, it is difficult to securely remove uniform and small toner particles with blade cleaning. Therefore, various kinds of methods for improving the cleaning property have been proposed by devising toner. One of such methods is to make a spherical form irregular. The form of toner is made to be irregular to reduce powder fluidity of the toner and hold the toner by blade cleaning. Characteristics of toner, for example, transfer quality, transfer efficiency and cleaning property, depend on toner form. Therefore, it is demanded to establish the method of making a toner form irregular.
In the emulsion agglomeration method, toner having an irregular form originating from its primary particles and the agglomeration thereof can be manufactured by agglomerating the primary particles of the emulsion polymerized resin particles. Furthermore, in the dissolution suspension methods and the suspension polymerization methods, in which a toner particle is made from an oil droplet, a method is known in which form irregularizing agents are internally added.
For example, unexamined published Japanese patent application No. (hereinafter referred to as JOP) 2005-049858 describes a method of making toner form irregular in which an inorganic filler, for example, silica, is contained inside toner to secure blade cleaning performance.
However, the blade cleaning achieved thereby is on the macro level and still needs improvement on the minute level.
There are two main indices to indicate the cleaning property. The first is bad cleaning performance A in which a cleaning blade does not hold toner completely and thus some toner remain on the surface of an image bearing member. This results in background fouling. The second is bad cleaning performance B caused by unstable movement of a cleaning blade nip portion. Toner slips through the cleaning blade only at the position where the unstable movement of the cleaning blade occurs in the width direction thereof. This results in fouling by streaks.
It is possible to reduce the bad cleaning performance A by making the toner form irregular, which is described above. However, this is not sufficient to reduce the bad cleaning performance B.
With regard to blade cleaning, various kinds of studies and development have been made, for example, “the friction index μ at the contact position of a blade and an image bearing member is desired to be low”, or “the torque of an image bearing member is desired to be stable with in a certain level”. The mechanism of the blade cleaning system is that toner is stopped and held at the nip formed between a blade one after another (this is referred to as dam effect). When there is a gap between an image bearing member and a cleaning blade due to flopping and/or stick slip of the nip portion of the blade, the bad cleaning B is deduced to occur. Namely, the contact state of the nip portion formed while an image bearing member rotates is unstable, the bad cleaning performance B occurs.
In a typical method of making a toner form irregular, aggregated bodies of inorganic filler particles is present on the surface of toner. In the case of the toner for use in the present invention, modified laminar inorganic minerals exist on the surface of toner, which has relatively good cleaning property in comparison with the typical method case. This is considered as follows: Since the toner on which aggregation bodies of inorganic filler particles are present has particle materials on the concave portions formed due to form irregularization, the toner particles are not easily engaged with each other so that a dam may not be formed.